Etching is widely used in the fabrication of semiconductor devices. A process for etching a pattern, e.g., a trench, in a semiconductor substrate usually starts with forming a mask on the substrate. The substrate is then etched through the mask, which defines the pattern etched in the substrate. Photo resist is typically used for forming the mask. In some processes, e.g., deep trench etching, the etch selectivity to the photo resist material is insufficient, and the etching process depletes the photo resist mask and damages the underlying substrate.
In such etching processes, a dielectric hard mask, e.g., a thick silicon dioxide or silicon nitride hard mask, can be used to effectively protect the underlying substrate. Patterning a thick dielectric hard mask requires a thick photo resist mask. However, forming small patterns in a thick photo resist mask is difficult because of the shrinking photolithography depth of focus. Thus, such etching processes are not suitable for fabricating high density and high performance semiconductor devices. In addition, silicon dioxide and silicon nitride are commonly used to form dielectric structures over a semiconductor substrate. Thus, removing the hard mask after the etching process often alters and/or damages the dielectric structures underlying the hard mask. This may adversely affect the performance, characteristics, and reliability of the semiconductor devices fabricated on the substrate. The dielectric hard mask can also be patterned using a silicon mask deposited thereon. However, the removal of the silicon mask often alters and damages the underlying semiconductor substrate, thereby adversely affecting the performance of the semiconductor devices fabricated thereon.
Accordingly, there exists a need for a process for etching a semiconductor substrate using a hard mask that does not adversely affect the performance, characteristics, and reliability of the semiconductor devices fabricated on the semiconductor substrate. More particularly, it is desirable to be able to remove the hard mask without affecting the underlying material on the semiconductor substrate. It is also desirable for the etching process to be simple and cost efficient. It would be of further advantage for the etching process to be compatible with existing semiconductor device fabrication processes and suitable of fabricating high performance semiconductor devices.